A quantum dot is consisted of a limited number of atoms, and has a three-dimensional size in the order of nanometer. Due to quantum size effects, light emitted by quantum dots has a very narrow width at half maximum, has extremely excellent color purity. By making the quantum dot material into a quantum dot light emitting diode (QLED), color gamut better than that in an organic light emitting diode (OLED) display device can be achieved.